Expected value of random variable which is the number of drawns required











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An urn has n balls and we take balls from it with replacement until each ball has been drawn at least one. X denotes the number of draws required. What is the expected value and variance of X?
I think X is at least n, is it true? And how should I find the expected value of it?






probability random-variables variance expected-value







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An urn has n balls and we take balls from it with replacement until each ball has been drawn at least one. X denotes the number of draws required. What is the expected value and variance of X?
I think X is at least n, is it true? And how should I find the expected value of it?






probability random-variables variance expected-value







share|cite|improve this question







New contributor




Egshiglen Bat-Erdene is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
















  • 1




    This is known as the coupon collector problem,
    – lulu
    9 hours ago










  • Thank you so much
    – Egshiglen Bat-Erdene
    9 hours ago













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up vote
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down vote

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An urn has n balls and we take balls from it with replacement until each ball has been drawn at least one. X denotes the number of draws required. What is the expected value and variance of X?
I think X is at least n, is it true? And how should I find the expected value of it?






probability random-variables variance expected-value







share|cite|improve this question







New contributor




Egshiglen Bat-Erdene is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











An urn has n balls and we take balls from it with replacement until each ball has been drawn at least one. X denotes the number of draws required. What is the expected value and variance of X?
I think X is at least n, is it true? And how should I find the expected value of it?






probability random-variables variance expected-value




probability random-variables variance expected-value






share|cite|improve this question







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Egshiglen Bat-Erdene is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|cite|improve this question







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Egshiglen Bat-Erdene is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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Egshiglen Bat-Erdene is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.








  • 1




    This is known as the coupon collector problem,
    – lulu
    9 hours ago










  • Thank you so much
    – Egshiglen Bat-Erdene
    9 hours ago














  • 1




    This is known as the coupon collector problem,
    – lulu
    9 hours ago










  • Thank you so much
    – Egshiglen Bat-Erdene
    9 hours ago








1




1




This is known as the coupon collector problem,
– lulu
9 hours ago




This is known as the coupon collector problem,
– lulu
9 hours ago












Thank you so much
– Egshiglen Bat-Erdene
9 hours ago




Thank you so much
– Egshiglen Bat-Erdene
9 hours ago















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